One type of display device operates by spatially modulating an output light beam and projecting the spatially modulated output light beam onto a display surface. The source of the output light beam may be of any operable type, but one common approach is to provide a metal halide lamp that produces the output light beam. Many different types of reflective and transmission spatial light modulators are known to modulate the output light beam with the desired visual information.
With increasing time of use, the output light beam of the lamp changes. The intensity may fade, reducing the brightness of the display. Eventually, the lamp fails (“burns out”), eliminating the displayed image entirely. Lamps are the one component of the display device whose performance is known to become impaired over a relatively short period of time in service, but the time associated with this impaired operation is not readily predicted with precision. Additionally, the lamp may be damaged while in service by shock loadings or the like, so that its light output is partially or completely lost.
In most applications, the degraded or failed lamp is readily replaced. There is a short period in which the display device is out of service when the lamp is replaced. The out-of-service period produces nothing more than a minor inconvenience.
In other applications, however, the loss of display brightness or complete loss of service, even for a short time, may be much more serious. For example, modern military forces rely heavily on data displays. The unacceptably high degradation or loss of service of a military display device in combat, even for a few minutes, may have disastrous consequences. Further, a military display device may operate with a sealed housing that makes it difficult or impossible to gain access to the interior of the device to replace the lamp while the display device is in combat service. If the light output of the lamp of such a display device drastically degrades or fails during combat, the display device becomes inoperable and essentially eliminates its user as an effective participant in the battle.
There is a need for an improved approach to display devices in which the lamp illumination source may degrade or fail in service. The need is particularly acute where impairment of the display device for any significant period of time may have major adverse consequences, and where the replacement of the lamp is difficult. The present invention fulfills this need, and further provides related advantages.